The present invention relates to maintenance work on live high-tension (up to 34- kv) electric power pole lines.
It frequently happens that a particular pole in a live three-phase power line must be converted to a terminal pole in order, for example, to feed a new industrial plant. In such case, the high tension line must be tapped at the top of a line pole. In such situation, it is desirable to do the work without interrupting the power in the line, since power interruptions cost the utility company loss of revenue. Moreover, service interruptions make customers unhappy.
Another example of a situation requiring clearing of the area at the top of the pole is where an insulator has cracked and requires replacement. In such case, the live high-tension wires must be disconnected from the crossarm and lifted by some means above the pole top to make room for the lineman to work without coming into physical contact with the live high-tension wires.
Heretofore, the live high-tension wires have been lifted by a temporary crossarm which is attached to a three-arm lifting tree. Such a tree has a central arm and on each side thereof a side arm. The side arms are connected to the central arm at the lower end but diverge outwardly at their upper ends. The central arm of the lifting tree is attached to the pole by several spaced-apart braces and, to lift the tree to raise the live conductors, the braces must be moved upwardly on the pole. Assembly of such a lifting tree, attaching it to the pole, shifting it and its braces upwardly as the tree is raised to lift the live conductors, requires several linemen and several hours of work.